Fork and steering assembly for bicycles

ABSTRACT

A light weight aluminum bicycle fork with positive feel and improved control in rough conditions, and is stiffer in torsional stiffness, fore and aft stiffness and side-to-side stiffness and has a higher overall rigidity than prior art forks. A large diameter steering tube has an hourglass external surface and bearing raceway seats formed therein and a very large diameter head tube has a corresponding bearing raceway seat formed in the lowered end thereof to receive, by way of a press-fit, aircraft-type torque tube bearings. An upper bearing assembly is seated in a raceway seat formed in the upper end of the head tube. Adhesive is used to maintain the bearings in position and prevent their loosening. A pair of large diameter crown miter tubes are welded to the lower end of the steering tube and a pair of large diameter, tapered, blade tubes are welded to the crown miter tubes and have dropouts welded to the lower ends of the blades. The blades utilize proportional tubing with metal located at specific locations on the wheel sides where maximum stress forces are found. A one-piece aluminum bar, neck and large diameter stem is provided. A tightening wedge and the stem have complementary camming surfaces which are at a shallow angle.

The present invention relates to improvements in bicycles, moreparticularly to the front fork and steering assembly.

BACKGROUND OF THE INVENTION

In my Patent U.S. Pat. No. 4,500,103 for a HIGH EFFICIENCY BICYCLEFRAME, very large diameter frame tubing is used in a bicycle to resistrelatively large torsional and bending forces to produce a bicycle whichis very light in weight yet extremely rigid and which, at the same time,provides an extremely good ride. In my Patent U.S. Pat. No. 4,621,827, Idisclose a bicycle in which the chainstay tubes are made of unequalrigidity and made in such a way so as to increase the power trainefficiency by reducing the magnitude of frame deflection caused by chainstress. The present invention is directed to improvements in thesteering and front fork assembly head set bearing and handlebar stem ofa bicycle.

The front fork of bicycles typically have been steel with about one inchsteerer (e.g., one inch outside diameter steerer post in steel). That iswhat the headset bearings and all the headset pieces were made toaccommodate and the one inch size was limiting in steel. The steelsteerer uses a fairly thick wall near the crown in order to make thefork strong enough.

In the bicycle described in my patent U.S. Pat. No. 4,621,827, the headtube had an outside diameter of about 1.42 inches and an inside diameterof about 1.180 and a center section wall thickness of about 0.065inches. In order to fit in one inch bearing size constraint in aluminum,a solid bar had to be used and it still is not strong enough because ofthe small diameter size.

In the past, on mountain bikes and on some road bikes, others havestarted promoting larger headset sizes with 11/4 inch steering tubes.This is still made of steel in order to make the forks more rigid forbetter cornering control but they are still essentially about the sameweight or heavier. There have been suggestions of aluminum forks. Theseuse a conventional headset and headset bearing units. Hence, the frontfork and headset assembly of a bicycle has been the heavy end of thebike and it has been the end that gets the most shock.

There has been introduced to the market a number of front forks which donot have curved blades but which have instead straight blades and thereis controversy in the bicycling art concerning whether these straightblades provide harsher riding forks or not. The present invention usesstraight blades.

The wheel axle is typically offset forward of the steering axis in orderto obtain desirable handling. This offset is called the fork rake. Thepresent invention uses a fork rake of about 11/2 inches.

Headset bearing failures are a frequent problem in off-road bicycles.The repeated impacts of off-road use brinell the bearings, loosen thebearing housings in the head tube and the fork crown, loosen and damagethe threaded adjustment mechanism. Because of angular misalignmenttolerances necessary for inexpensively machined steerer crowns, headtubes and adjusting threads, the traditional bearing assemblies use acup and cone system, where the radius of curvature of the balls is muchsmaller than that of at least one of the raceways. This allows thebearing to tolerate angular misalignment and substantially reduces thecontact area of the balls, compared to the Super Conrad stylebearing--with raceways closely fitted to the balls. The rigidity of thepoint contact style bearings is thus substantially lower than that ofthe torque tube type bearing and the load carrying capacity is very muchlower. This invention is able to fully utilize the advantages ofdouble-sealed aircraft torque tube type bearings by machining theoutside diameter of the steering tube for direct fit and adhesivebonding of the headset bearings to the external surfaces of the steeringtube and raceway seats in the head tube, insuring accurate alignment.The ends of the head tube are also precision bored for alignment, andalso benefit from direct fit. The threaded adjustment of traditionalheadsets is another source of trouble. The threads weaken the thin wallsteering tube and can break there, especially if the handlebar stem isclamped inside the threads.

The invention results in a bicycle front end which does not requirefrequent adjustment or services with far greater durability, and isdirected to improvements in the front fork and headset and steeringassembly and is particularly directed to the utilization of very largediameter aluminum tubing, a unique headset bearing assembly. Accordingto the invention, the fork blades are greater than about 11/2 inch indiameter at the top and about 11/8inch at the fork ends down at the tip.They are, in the preferred embodiment, rounded all the way: they arestraight for a predetermined distance and then they taper and have awall thickness proportional to the forces or loading at specificlocations on the blades.

Each blade is mitered at the crown end at an angle and a speciallyconfigured crown tubing is mitered to fit up against the blade. It isvery difficult to bend the big tube easily and have a tight radius so inthe disclosed embodiment the large diameter aluminum tubing is miter cutand welded.

Furthermore, instead of using a conventional headset, a steer tube ofabout 15/8 inch diameter was utilized and the part that goes up throughthe bearings is about 1-9/16 inch so that the steer tube is actuallyabout 1-9/16 inch. The outside diameter of the bearings is about twoinches so that the head tube has a diameter of about 21/4 inches at thetop and bottom to provide raceway seats to fit the bearings and thebearings are pressed fit and adhesively bonded right to the head tubeand to the steering tube. In this present application, the steerer tubehas been machined to locations where the stress or forces are less andtapered to the bearing seats where the tube wall is thickened.

This extremely large diameter head tube along with the large diametersteering tube or post provides a more positive control in roughconditions and is significantly stiffer in both torsional stiffness andfore and aft stiffness and side-to-side stiffness than traditional oneinch steerer forks and has essentially the same rigidity as the morerecent larger 11/4 inch forks. Moreover, the weight is significantlyless than any prior art fork and steering assembly having equivalentrigidity.

The crown piece according to this invention is much larger than thatused in a regular fork. With this in mind, if standard headset bearingsare used, the front end of the bike is elevated in the air e.g., thestack height is exaggerated. Hence, instead of using a conventionalheadset, this invention utilizes about 15/8 inch steer tube and the partthat goes through the bearings is about 1-9/16 inch diameter so that ineffect a machined to about 1-9/16 inch steer tube up through thebearings and forms a shoulder or raceway seat. As noted above, thesteering tube has had metal machined at points of lower stress orloading to reduce weight without sacrificing strength and safety. Theoutside diameter of the bearings is about two inches. The upper andlower bearing raceways are further secured in place with an adhesive,preferably an anerobic adhesive but epoxy adhesives can also be used.

Further, according to the invention the handlebar, neck and stem areunitized and designed to accommodate the larger head tube and steer tubediscussed above. In a preferred embodiment, the stem is about 13/8inches in diameter and has a wall thickness of 0.070 inches and alighter stem and handlebar. This again adds to the positive feel andcontrol on it and the ride is very good notwithstanding the fact thatthere is reduced flex in the front forks. It is believed that the largeflex in the front fork is not necessary because when going over roughterrain and the front wheel for example, hits a bump, the fork beingangled towards it the flexible fork will flex backward and in flexingbackward bumping the front end of the bike to jack it up in the air in apogo-stick-like effect. This increases the actual vertical movement overwhat occurs with a stiff rigid fork as is disclosed in the presentapplication. The stiff fork reduces the degree of bounce so that whenyou hit a bump, instead of the fork flexing back and raising the frontend of the bike and causing it to loose contact with the terrain, thefork does not flex back and the tire seems to deflect more. According tothe invention, the tire is made to work harder and the bike stays ontrack better. That is, the bicycle stays on the ground and control isbetter and the feel is good and the bicyclist has a feeling of being incontrol on it, which is very useful. Moreover, the cyclist can go at ahigher speed because of having more control, and the traction seems tobe better particularly on downhill runs.

The invention has been applied to a mountain bike but it is believed tobe just as applicable to road bikes. However, the road bike fork tubingneed not be quite as large as the mountain bike, it can be made lighterand use a smaller headset size and smaller blades for cosmetic and airresistance reasons.

The overall effect is to reduce the weight of the front end of the bikeby about a pound and one-quarter to about a pound and one-half. Theheadset is lighter, the front fork is much lighter and the handlebar,neck and stem are likewise lighter. This is due in part to the fact thatit is a one-piece handlebar and stem that weighs no more than other highquality stems on the market. It will be noted that the fork according tothis invention, will only fit a bike made with the larger head tube.Hence, the invention takes a special frame and a special head tube toadapt to it. Normally new fittings are required. Aircraft torque tubebearings from the bearing assemblies are used. The threads that areneeded to adjust the bearings have been eliminated because the bearingsare direct press and adhesive secured bearings and no threads areneeded. This type bearing adds to the positive feel and control obtainedin bicycles according to the invention because they have a lot morerigidity in the torque tube bearings than normal bike bearings have.Placing the bearings inside the head tube strengthens the bearing jointsfor the head tube.

The present invention deals with the proportional tubing utilized in thefork blades. In the prior art, the blades typically used a straight tubewhich is the simplest design wherein the uniform wall for each tubeincreases the wall diameter until the tube has sufficient strength totake all loads and load concentrations. However, this results in a veryheavy tube. Butted tubes utilize thin-walled tubes in the center andheavier walls at each end. Stresses are cantilevered at the tube endswhere they join with the other tubes. The walls are able to take higherjoint stresses while the thinner section allows reduced weight. Thereason for proportional tubing, in bicycle frame design, is that thestresses in the tubing cantilevered toward the ends, but the actualworking loads are not uniformly distributed around the circumference ofeach frame tube. In the main frame, in the region of the head tube, thelargest loads are the result of high vertical landing loads and head-onimpacts. Thus the top and bottom surfaces of the frame tubes see muchhigher loads than the sides. As known in the art, a more efficient useof material is to reinforce the top and bottoms to special dimensions ofthe tube (other than round) or increased wall thickness at the top andbottom of the tube, or the combination of the two.

In the front forks, the normal loading includes some torque loads andsome side loading. The heaviest loads will come from vertical bumps orhead-on impact and/or braking forces. Both vertical and longitudinalforces stress the front fork at a fore/aft cantilever bending motion. Ina simple analysis, it appears that increasing the strength of the forkblades and steerer fore and aft cantilever would be the correctapproach.

However, it has been discovered through actual testing and detailedanalysis that forces in the fork blades are displaced to the side wherethe steerer attaches, or the wheel or inside of the fork, a smallamount. Thus, the optimum here, according to the invention, is not adirect fore and aft reinforcement, but two reinforcements (e.g. thickerwall) are shifted slightly to the inside of the fork as can been seen inthe drawings attached hereto. Another factor is that there is a highdegree of compressive stress resulting from the vertical bump loading.Thus, in the preferred embodiment, the front of the blades is reinforceda little bit more (e.g., thicker wall and more metal) than the rearbecause of the straight compressive stress and the cantileveredcompressive stresses are cumulative in the front of the blade and opposeeach other in the rear. Thus, there is a slight differential in thethicknesses in these areas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, advantages and features of the inventionwill become more apparent when considered with the followingspecification and accompanying drawings wherein:

FIG. 1 is a front sectional view through the front fork, head tube andheadset bearings incorporating the invention and FIG. 1b is an enlargedportion thereof,

FIG. 2a is a front view of the lower end of the fork blades (the spacingbetween dropouts has been reduced) showing the dropout incorporating theinvention, FIG. 2b is a sectional view through lines 6--6 of FIG. 2a,

FIG. 3 is a side view of the dropout according to the invention,

FIG. 4 is a front view of the bar and oversized stem incorporated in theinvention,

FIG. 5 is a top view of the bar and oversized stem incorporated in theinvention,

FIG. 6a is an enlarged sectional view through lines 6--6 of FIG. 4,

FIG. 6b illustrates the tightening wedge in section,

FIG. 7 is a side sectional view of a front fork in which the fork bladesinclude the proportional tubing according to the invention,

FIG. 8 is a front view with a sectional portion of the front blade andsteerer tube illustrating the principles of the present invention,

FIG. 9 is a sectional view of proportional tubing incorporated in theinvention,

FIG. 10 illustrates the dimensional aspects of the tubing in anexemplary example thereof, and

FIG. 11 shows the steerer tube and portion of the head tube according tothis invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1a, and 1b, the fork and head tube assembly isillustrated in section with the head tube 10 having a large internaldiameter of about 17/8 inches (in this preferred embodiment) and uniformthroughout the length of the tube and an external diameter or OD of 2inches in the central body portion thereof and thickened to about 21/4inches OD at each end. In this embodiment the overall length of the headtube is about 6 inches (which obviously depends on the frame size). Theupper end 11 and the lower end 12 of head tube 10 are thicker than theintermediate central body portion with the internal upper edge 13 havingan annular shoulder formed therein to form a top raceway seat 14 and thelower end likewise provided with an annular shoulder to form a lowerraceway seat 16. Aircraft control or torque tube bearings 18 and 19 arepress fit into raceway seats 14 and 16, respectively and an adhesive,preferably an anerobic adhesive, is used to permanently maintain them inplace. These are super strong and durable double-sealed aircraft controlor torque tube bearings which have a long life and are capable of takingat least 3200 pounds of thrust, 6800 pounds of radial load capacity perbearing. The arrangement just described provides a headset bearingarrangement which does not require any threads which loosen and/or getdamaged thereby securing said headset bearing and front fork in placesolely by adhesive bond. It provides a super lightweight headset with aminimum stack height. The adhesive also isolates the steel bearingraceways from the aluminum and seems to help reduce corrosion. It shouldbe noted that years of experience of use of a anerobic adhesive in thebottom bracket bearings has borne this point out.

The front fork (constituted herein by steering tube 21, short crown tubemiter pieces 30, 31, straight blade tubes 35, 36 and tapered blade tubes37, 38 and dropout 38D, 39D) is made of large diameter, shock absorbingheat treated aluminum construction and provides positive steeringcontrol, is ultra light super strong in design and has a large tireclearance. Specifically, the steering tube 21 is extraordinarily largein diameter compared to prior art steering tubes (some of which are aslarge as 11/4 inch, as noted above). In this invention, the lower end ofthe steering tube just above the crown portion is provided with a bottomrace seat or annular shoulder 22 which seats the inner race of the lowerheadset bearing 19. Thus, the loading from the front wheel istransmitted through the upper and lower bearings to the head tube,providing a very short stack height. By putting the bearings inside thehead tube in the manner illustrated in FIG. 1, and using an adhesive tosecure the bearing raceways in place at the head and steering tubes, thebearing joint for the head tube is significantly strengthened and thestack height reduced. The upper end 21U of steering tube 21 may beprovided with a large diameter seal member (not shown).

As shown in FIG. 1, the internal lower end of the steering tube ismachined to have a slight taper, and the outer diameter of the upperportion of the steerer tube is completely machined.

The lower end of steering tube 21 has welded thereto a pair of laterallyextending crown miter pieces 30 and 31. These are large diameter roundor ovalled tubes having the same diameter as the upper straight ends 35and 36 of the fork blades. Crown pieces 30 and 31 have their lower endsmiter cut to form the angles indicated and are heliarc welded to thesteering tube and to the upper ends of the respective blades 35, 36. Theends of crown miter tubes 30 and 31 are shaped complementary to thecurvature of the head tube so that when heliarc welded to the lower endof steering tube 10, it results in a very strong and rigid joint. Afterthe final weldments are made, the fork unit is heat treated to a T6condition.

In the embodiment illustrated, the length of the straight blade sectionof about 15/8 inch aluminum tubing is, on the outer periphery of about43/8 inches and, on the inner periphery 3-7/16 inches. At the lower endof the tubes 35 and 36, the upper ends of tapered tubes 37 and 38 arewelded thereto. These taper from about 15/8 inch, as illustrated down toabout 11/8 inch diameter and have the wall thickness tapering from about0.058 inches at the crown to about 0.049 inches at the dropouts. Thesealuminum tubes with their given dimensions provide a very rigid superstrong design with shock absorbing heat treated aluminum constructionand thereby provides positive steering control with minimum lateral(sideways) flexibility, with maximum cornering and traction and control.It provides super rigid brake mounts (not shown) and a very large tireclearance in an ultra lightweight fork design.

The dropout design is illustrated in the front view of FIG. 2a, which isan enlarged view of the dropouts. (In this enlarged view, the left andright blades have been moved together.) It will be noted that thecurvature of the upper end 38U, 39U of the drop out members 38D, 39D arecurved and the lower ends of tapered tubes 37, 38 are complementarycurved to provide, when the dropouts are welded in place, a very strongjoint. The dropouts 38D, 39D have curved upper ends which have a "U"shaped positioning ridge or lip 39L and are heliarc welded into thecorrespondingly curved lower ends of the taper tube portions 37, 38,thus completing the blades for the front fork. U-shaped notches 40receive the front wheel axle. (The letters "L" and "R" correspond toleft and right.)

FIG. 4 is a front view of the bar 50 (which has tapered walls), stem 51,neck 52 and tightening wedge 53. Neck 52 is shaped at each end joiningtube and tapered wall bar 50 for strength and lightweight. The bar 50 iswelded to neck 52, which, in turn, is welded to stem 51. Thesecomponents are made of 6061 aluminum, which is heat treated to a T6condition after welding. Tightening wedge 53 is made of 7075, T6aluminum. The camming surfaces 51S and 53S have an angle which is muchshallower (20 degrees or less) than in the art. This results in a longerwedge 52 and much better grip surface and more holding power on theinternal surfaces of steering tube 21. A small diameter (6 mm) threadedlong bolt 54 is used to draw tightening wedge 53 against mutuallycamming surfaces on the wedge and stem. Note that the stem 51 andtightening wedge 53 are of large diameter and include a longer largediameter clamping wedge for more evenly distributing pressure to providea tighter grip with less force.

The cam surfaces 51S on stem 54 according to this aspect make the wedge53 operative over 2 inches in actual clamping length. This is thedistance the two mating wedge surfaces 51S and 53S are in contact alongthe axis. Some wedge parts may extend beyond the bottom edge of the stembut this extra length of contact is not balanced and creates even morehighly concentrated stress points higher up and in the preferredembodiment is not desirable. By spreading the load along the axis, thestem is held much more securely, with lower concentration of stress onthe steering tube 21. Traditional stems have an effective clamp lengthof less than one inch, with a typical ramp angle of about 35 degrees.

Another advantage of the longer wedge comes in the bending momentsapplied to the stem from the handlebars. The side-to-side andfront-to-back bending loads need to be rigidly transferred to the forksteerer in order to prevent metal fatigue, fretting, or loosening of theclamped assembly. The standard stem fits into the fork steerer with somedegree of play, usually on the order of about 0.005 inch but it has beenmeasured over 0.010 inch in some cases. With play in the top portion ofthe machined stem, the only place it fits tightly into the fork steereris at the wedge clamp location, where the wedge is expanded to fit.Thus, the side-to-side flexing of the stem applies a bending moment tothe wedge area. The preferred configuration with the 2 inch length ofclamp, gives greatly increased resistance to the bending moments thanthe traditional shorter clamp assemblies. The ramp not passing all theway across the stem diameter also increases the amount of surfaceactually being applied to clamping forces.

The traditional stem wedge bolts are 8 mm diameter by 1.25 mm threadsteel Allen socket head cap screws. Combined with the typical 35 degreewedge angle, the clamping is marginal, as the ramp exerts about a 1.4multiplier of bolt tension to radial clamping force (under idealconditions).

The preferred configuration according to this aspect, in the traditional0.875 inch size, uses a 6 mm diameter by 1 mm thread steel allen sockethead bolt 54 combined with a 16 degree wedge angle, and long clampinglength. Although the bolt 54 has only 56 percent of the cross sectionalarea of the traditional size, and thus somewhat reduced strength (it ispreferred to use a higher grade of bolt than normal which somewhatcompensates) the 16 degree ramp angle of the 0.875 inch model exertsabout a 3.5 multiplier of the bolt tension to radial clamping force(under ideal conditions). This gives more than twice the availableradial clamping force over the traditional stem and wedge assembly.

The preferred configuration, in the new super size 1.375 inch diameter,also uses the 6 mm diameter stem bolt 54, but with about a 20 degreewedge angle. The 1.375 inch stem 51 utilizes a thin 0.070 wall. Thewedge 53 also uses a similar thin wall tubular design, unlike solidwedges of other manufacturers. The thin wall still achieves very highstrength because of the large diameter design, but at greatly reducedweight. The 20 degree wedge angle exerts a multiplier of about 2.7 timesbolt tension, but the twisting torque required to spin the stem isincreased because of the increased moment of the larger stem and forksteerer diameters. The larger 1.375 inch diameter stem 51 has 1.6 timesmore torque resistance for the same radial clamping force as compared tothe traditional 0.875 inch diameter stem. This, in combination with thewedge angle multiplier of 2.7 times, gives a torque multiplier of 4.3(under ideal conditions, i.e., equivalent coefficients of friction,lubrication and so forth). Again, this feature of the invention achievesmore than twice the available resistance to torque over the traditionalstem and wedge assembly.

The stem clamping must be able to keep the fork steerer from twisting orsliding under normal operating conditions. When the bike is crashed,however, if the stem slips under crashing stress inside of the steerer,it may keep some other damage from occurring. Thus, the ideal stemclamping system would have enough clamping friction to hold it in place,but when stressed unusually hard, be able to slip without damage toeither stem or fork.

Traditional stems have caused many fork failures. The highlyconcentrated pressure of the small wedge or expanding cone in the priorart will expand, bend or even cause the fork steerer to crack. Some ofthe wedges are made with teeth, serrations or other roughening means inorder to effect a more secure grip on the fork steerer. But when thebike is crashed and the clamp is forcibly moved, the teeth gouge theinside of the fork steerer, damaging it. The stems tested that use thesurface that bites into the steerer are able to generate enough clampingpower in order not to slip under normal off-road conditions (includingtrails with rocks, logs and roots to ride over). Riding in theseconditions requires much more torque to be applied to the fork steererthan would be required on a road bike. In general, the stems ofconventional nature with a smooth wedge may slip while riding over arock or root where some torque is input in order to keep the front tiregoing in the desired direction. When the stem slips in this condition,the rider generally falls.

The present invention fork, with a fork steerer made of aluminum, wouldbe particularly sensitive to this type of damage. The 1.375 inchdiameter stem, with greater than two inches of clamping length, resultsin stress concentration three to four times less than traditionalclamps. The surfaces of the wedge and stem are smooth, and the clampingis more secure than a traditional stem.

The wedge 53 is long, and unlike traditional stems, does not cutcompletely across the stem, but stops about two thirds of the way acrossit.

The invention achieves a fine balance of the need for rigid, reliableclamping with the ability to slip under extreme force without damage tothe system. This is especially important when using the aluminum alloyfork steerer of the preferred configuration. Further the design achievesvery lightweight and high rigidity and strength with the large diameterwelded and heat treated one-piece design.

As discussed above, different sections of a bike frame are subjected todifferent stress loads. More specifically, different sections of asingle-frame tube are subjected to different stresses. This fact isused, according to the invention, to eliminate weight while addingstrength. According to this invention, the wall thicknesses of the forkblades in particular areas or spots, where high stresses or maximumforces have been discovered, is in direct proportion to the force thatthe area or spot will see or use. While the general concept ofincreasing the metal thickness in areas of frame where the maximumstresses occur is known, in the present invention, it has beendiscovered that in the fork blades the stresses are offset from normalfore and aft (front/back) axis.

Referring to FIGS. 7-11, and particularly to FIG. 10, the optimumpositioning of the metal is not in a front/back or fore/aft directionbut, rather, the two reinforcements are shifted axially to the wheel orinside. (In FIGS. 7-11, corresponding parts corresponding to earlierfigures are identified by primed numbers.) In FIG. 10, the tubing 100initially begins as a straight tube and then having the sectionillustrated in FIG. 10 and then the lower ends is spun in a manner to bedescribed later herein to produce thicknesses illustrated in FIGS. 7 and8. FIG. 9 illustrates a left blade, and FIG. 10 illustrates a rightblade on a fork, the rib 101 being aligned with the front of the forkand the front of the bike.

As illustrated in FIG. 10, the tubing 100 has a rib 101 which isbasically a guide rib for the spinning operation but also is used forlocating as a point of reference the different angular positions on thetubing. As illustrated, guide rib 101 is behind the direct front edgesurface of the blade, the outside edge surface is designated by 102, andthe wheel or inside edge surface is designated at 103, and the trailingedge surface is designated at 104. At about 20 degrees from the frontedge surface is found the maximum stress or force and here is locatedthe maximum thicknesses (of about 0.09 inches) and at about 60 degreestherefrom and, extending for about a 20 degree space is a low stresssector and a thin portion of the tubing (0.049 inches) and this extendsfor this 20 degree sector. Then 60 degrees farther (going clockwise) isthe next largest thickness portion which is at about 0.085 inches. Notethat to each side the thickness gradually increases from the thinnersections (0.049) to the thickest portion (0.09 and 0.085). Thus, themaximum stresses in the fork blades are at the positions indicated atMS1 and MS2 and the least stress is directly at the wheel side and onthe outside, where the metal is made thinner. The two 120 degree sectorsof reinforced tubing accommodate the maximum stress areas MS1 and MS2,respectively. In FIG. 7, these reinforcement dimensions arediagrammatically illustrated on the front and back sides but they havethe displacement illustrated in FIG. 10. That is to say, the maximumthickness of the fork blade is positioned about 20 degrees to the wheelside from the front edge of the blade or from guide rib 101. Similarly,the next second maximum point of stress is the MS2 which is positionedat about 140 degrees from guide rib 101. Note again that the metalgradually thickens from the minimum thicknesses (0.049 inches) to amaximum thicknesses (0.09 and 0.085 inches, respectively). This producesa tubing in which the tube wall thickness in a particular spot orlocation is in direct proportion to the force that that spot will see inuse.

As shown in FIG. 10, guide rib 101 is behind what is to become the frontsurface of the FS of the blade and about 20 degrees to the inside orwheel side is spot or area MS1 where the maximum stress or forces willbe applied and the wall thickness is greatest at this point. The wallthickness gradually decreases from spot MS1 for about 60 degrees to eachside thereof to where the the wall thickness 0.049 inches) is thinnest.What becomes the wheel side WS 103 (a space of about 20 degrees) and theoutside OS 103 having a space of about 100 degrees (having a wallthickness of about 0.049 inches). A similar gradual thickening from thetrailing ends of wheel side 103 to the trailing end of the outside edge102. This inside trailing or aft edge 104 is gradually thickened to thespot or area MS2 of second highest stress where the wall thickness isabout 0.085 inches. This proportional placing or positioning of metalaccording to the in use loading stress or forces on the wheel side ofthe fork blades permits a reduction in weight, since the most metal isused where it is most needed, and at the same time, assures a higherdegree of safety.

To fabricate the fork blade a length of tubing, having the section shownin FIG. 10, sufficient to form a left and a right blade is cut in themiddle. Left and right blade mandrels (not shown) are used to shape eachblade to the internal shapes shown in FIGS. 7 and 8. Each tubing is slidonto its left or right mandrel and clamped thereto with each mandrelhaving a rib guide groove therein for receiving guide rib. The mandrelsare mounted in a lathe and a roller is run down the mandrel to spin thelower ends of the fork blades to the taper. This forces the metal in thelower portion of the blade (towards the dropouts) down to the mandrel toput the taper in (with the exemplary dimension (0.040 inches)illustrated in FIGS. 7 and 8). The tubes are cut to proper length forreceiving the dropouts and mitered at their upper ends for welding tothe crown miter tubes (which, in this case are made of tubing having0.095 inches thickness). The upper blade portions are straight and donot have the taper.

Conventional brake pedestals or posts BP are welded onto the blades.

In FIGS. 7 and 11, a similar concept is applied to the steerer tube,which in this preferred embodiment has a somewhat hour-glassconfiguration on the external surfaces where the location of where thebearing seats BS1 and BS2 have increased thicknesses of metal and themetal therebetween has been machined-down to reduce the amount of metaland hence the weight in these locations. Annular rubber seal rings SR1and SR2 protect the bearings from water, etc.

It will be apparent to those skilled in the art that other variationsmay be made within the scope of the invention. It is intended that theabove disclosure shall be read as illustrative.

What is claimed is:
 1. In a lightweight bicycle fork having a steerertube having upper and lower ends and a pair of hollow blade tubes havingupper and lower ends with the upper ends secured by crown means to thelower end of said steerer tube, and dropouts welded to the lower ends ofsaid blade tubes, said blade tubes having a fore and aft line bisectingfore and aft surfaces thereof, and wheel side portions adjacent a wheelmounted in said dropouts, and non-wheel side portions, the improvementwherein said hollow blade tubes have walls of variable thickness andwherein the thickness of material in said hollow blade tubes in highstress areas on said wheel side portion is greater than said non-wheelside portion in portions having lower stress, and wherein the materialforming the walls of said hollow blade tubes gradually thickens from afirst thin section about 40 angular degrees into said non-wheel siderelative to said fore and aft line to a thickest section about 20angular degrees on the wheel side of said fore and aft line and then thewalls of said hollow blades tubes gradually thin down to a second thinportion about 60 angular degrees from said thickest portion.
 2. Theinvention defined in claim 1 wherein said material forming said hollowblade tubes gradually thickens from said second thin portion throughabout 60 angular degrees to a second thick portion and then graduallythins to a third thin portion.
 3. In a lightweight bicycle having aframe with a head tube having upper and lower ends, a front fork havinga steering tube having upper and lower ends passing upwardly coaxiallythrough said head tube and at least a pair of head set bearings, saidhead set bearings rotatably connecting respective upper and lower endsof said head and steering tubes, the improvement wherein said steeringtube has a variable external diameter and exterior surface and whereinthe external diameter of said steering tube is greater than 11/4 inchesand the exterior surface is machine smooth, each of said headsetbearings having raceways which are fitted to and adhesively bonded inplace between said head tube and said machined smooth steering tube saidfork including a crown welded to said steering tube, including racewayseats machined intermediate the upper and lower ends of said steeringtube so that the exterior surface of said steering tube has an hourglassconfiguration, and bearing raceway seats machined at the upper and lowerends of said head tube for receiving said head set bearings,respectively.
 4. In a lightweight bicycle having a frame with a headtube having upper and lower ends, a front fork having a steering tubehaving upper and lower ends passing upwardly coaxially through said headtube and at least a pair of head set bearings, said head set bearingsrotatably connecting respective upper and lower ends of said head andsteering tubes, the improvement wherein said steering tube has avariable external diameter and an exterior surface and wherein theexternal diameter of said steering tube is greater than 11/4 inches andthe exterior surface is machined smooth, each of said headset bearingshaving raceways which are fitted to and adhesively bonded in placebetween said head tube and said machined smooth steering tube, includingupper and lower raceway seats machined in said steering tubeintermediate the upper and lower ends thereof, raceway seats machined atthe upper and lower ends of said head tube for receiving said head setbearings, respectively, said head set bearings being double sealedtorque tube bearings.
 5. The bicycle defined in claim 4 wherein saidfront fork is made of aluminum and has a crown and a pair of blades,said crown being constituted by a pair of round miter tubes each havinga pair of mitered ends which are welded to the lower end of saidsteering tube, said pair of blades having mitered ends welded to therespective ends of said round miter tubes and having walls of greatermetal thickness at points of maximum stress, dropout members welded tothe lower ends, respectively of said blades and a positioning lip on thesurface of said dropout.
 6. The bicycle defined in claim 4 wherein saidhead tube has an outside diameter of about 2 inches, said machinedsmooth steering tube has an outside diameter of about 1-9/16 inches,said bicycle further comprising a stem having a diameter of about 13/8inches and a lower end, a tightening wedge including a straight, shallowangled cam surface on an upper end of said tightening wedgecomplementary with a cam surface on the lower end of said stem and abolt for drawing said tightening wedge upwardly so that said camsurfaces cause internal gripping of said steering tube by said stem andtightening wedge.
 7. The bicycle defined in claim 4 including analuminum handlebar and a neck, said handlebar being welded to said neckand said neck in turn being welded to the upper end of said stem.